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Abstract Poplars and their hybrids are widely planted in both plantation forestry and agroforestry systems of the world. Along with the utilization and plantation management processes, a large amount of biomass residues are produced, but the relationship between biochar properties and soil CO2 emissions is largely unknown. Here, a laboratory incubation study was conducted to assess the effects of different biochars and their corresponding biomass residues on soil CO2 emissions during the 180 days of incubation. Poplar residue‐derived biochars were larger in the surface area and total pore volume but lower in nutrients and pH values than the rice straw‐derived biochar. Increasing pyrolysis temperature led to a decrease in the total nitrogen (TN) content of poplar leaf‐ and rice straw‐derived biochars, but enhanced the TN in the poplar twig‐ and poplar bark‐derived biochars. After 180‐day incubation, the total cumulative CO2 emission decreased by 33.1%–73.8% in the biochar amendments compared to their corresponding biomass residue addition, whereas the biochars derived from poplar twig and bark residues had more positive effects on reducing soil CO2 emissions, but depended on the pyrolysis temperature. Correlation analysis showed a significant and positive correlation between the CO2 emissions and TN content of bio‐based materials but the negative relationships to total carbon content and C/N ratio. Meanwhile the positive correlations of CO2 emissions to the surface area, t‐plot micropore area, and volume of the biochars were detected. Our results suggest that application of poplar twig‐ and poplar bark‐derived biochars has a great potential for mitigating global warming.

Cyclocarya paliurus is a well-known multifunctional tree species and its leaves are in especially high demand for tea production and medical utilization in China. To meet the enormous requirements of its leaf production, lots of C. paliurus plantations have been established for harvesting the leaves, producing a large quantity of pruning residues during their management. In this study, biochar at different pyrolysis temperatures (300 °C, 500 °C and 700 °C) were prepared, utilizing the pruning residues, and the effects of biochar additions pyrolyzed at different temperatures on soil properties, growth and leaf secondary metabolite accumulation in C. paliurus were investigated. The results showed that the chemical properties and FT-IR spectra of wheel wingnut-based biochar were significantly influenced by the pyrolysis temperatures, and the application of biochars pyrolyzed at different temperatures significantly affected soil pH and nutrient availability, as well as the growth, nutrient uptake and secondary metabolite accumulation of C. paliurus seedlings (p < 0.05). Correlation analysis indicated that the total contents of polyphenols, flavonoids and triterpenoids in C. paliurus leaves were negatively correlated with the contents of total phosphorus (P) and total potassium (K) in the leaves, but positively correlated with the ratios of carbon (C)/nitrogen (N) and C/P. After 200 days of biochar treatment, the highest biomass production and leaf secondary metabolite accumulation in C. paliurus were obtained in the addition of biochar pyrolyzed at 500 °C. The findings from this pot experiment provide a potential application in C. paliurus plantations, though long-term field experiments are required to optimize the quantity of biochar addition, based on soil conditions and stand age at the planting sites.